Nano in Nature
How can we
be covered in
water and
not get wet?
To answer this question,
nanoscientists turned to the
lotus flower.
It was noticed that the striking white
flowers of the lotus plant stayed dirt
free and dry even after being
submerged in muddy river water.
This helps the lotus in two ways:
•
•
Stops bacteria sticking to the surface.
Keeps the lotus cool.
How does the lotus keep clean?
The Lotus leaf has two
interesting features:
•
The surface of the
leaf is covered in a
waxy material which
makes it water
fearing or
hydrophobic.
To understand
the second feature we have to take a
And
closer…
closer
still…
closer look…
• The surface of the lotus leaf is actually quite rough.
• The projections increase the surface area reducing the amount of
contact water droplets have with the surface.
When
water falls on
of a leaf and
it clumps
form
The combination
of the
the surface
waxy coating
roughtogether
surfacetoallow
large
droplets.to roll right off taking dirt and micro-organisms that
the droplets
sit on the surface with them.
How does this benefit us?
We can create surfaces that stay dry and clean in the
same way as the lotus leaf.
Self cleaning windows
Waterproof clothes
But some animals are doing the opposite!
• Instead of shedding water the
Namib Desert Beetle uses
nanostructures to capture it.
• A combination of hydrophilic
ridges and hydrophobic
furrows allows collection of
moisture from fog.
• By applying this idea to
buildings we could trap
moisture and use as a water
source.
What do you
need to walk
upside down
on the
ceiling?
To answer this question,
nanoscientists turned to the
• Geckos have the
amazing ability to cling
to any surface at any
orientation.
• This is due to the
structure of their feet
which maximises surface
area.
A closer look
• The soles of geckos’
feet are made up of
overlapping lamella.
• These lamella are
covered with tiny
hairs called setae.
• Each setae branches
out into hundreds of
spatula shaped
structures.
How does a gecko stick?
• Most
Geckos’
surfaces
feet are
when
flexible
you look
enough
at them
to fit into
appear
the nooks
smooth
and
but
at a molecular
crannies
of any level
surface.
they can be quite rough.
•• At
such close
contact,
attractionall
called
‘Van der
Objects
may look
like forces
they’reoftouching
the surface
but
Waals’
they areforces
not. arise between the setae and the surface
creating grip.
Gecko glue
• Scientists are taking inspiration
from the nanofibres in geckos’
foot hairs to develop
adhesives that will bind to
wet and dry surfaces.
• Adhesives made from carbon
nanotubes which imitate the
setae on geckos’ feet have
been developed.
To answer this question,
nanoscientists turned to the
Can we make
fibres
stronger
than steel?
How strong is spider silk?
• Very strong!
• It is the material with the highest
known strength, about 5 times
that of steel of the same weight.
• It is also elastic; spider silk
can stretch up to 10 times its
own length.
More about spider silk
• Spider silk is produced
from about six silk
glands beneath the
spider’s abdomen.
• The silk consists of
protein molecules, long
chains comprising
thousands of amino-acid
elements.
• The protein is formed as
a liquid by silk glands
and squeezed out -the
liquid thread hardens as it
leaves.
Spider goat?
• Reports that goats have
been genetically
modified to secrete silk
proteins in their milk.
• The milk from the goats
was made into a superstrong silk strand.
• The thread could be
weaved to make strong
materials.
Caterpillar cocoons
• The fibres in caterpillar
cocoons are almost as
strong as steel.
• In CRANN, researchers
are taking inspiration from
these cocoons.
• They are synthesising
fibres that are stronger
than steel but 5 times
lighter - by mixing plastic
(PVA) with carbon
nanotubes.
What type of materials?
• Ultra-tough bullet-proof vests.
• Sports equipment.
• Aeronautics industry.
• Car parts.
• Household goods.
To answer this question, nanoscientists
turned to the
How is light
manipulated at
the nano-scale?
But first colours…
• Colours of some materials are determined by a
chemical pigment that absorbs some light
and reflects the rest (“chemical colour”).
• For example, chlorophyll in plants absorbs light
in the blue and red part of the spectrum but
reflects green.
• This is why leaves appear green.
Physical colour…
• An object can change colour when the light interacts with the
physical structures (“physical colour”).
• When light waves strike a
transparent surface some of the
light is reflected. A few light
waves penetrate the material
and reflect off the bottom of the
surface. These waves pass
upwards and re-join the original
waves.
•• When
When the
the crests
crests of
of the
the reflected
reflected waves
waves
do
they
‘outand
of phase’ and
linenot
upline
theyup
are
‘in are
phase’
destructive
constructiveinterference
interferenceisisobserved.
observed.The
waves
cancel
each other
out colours
and colours
The waves
combine
and the
appear
appear dimmer.
brighter.
The Morpho butterfly
• The extraordinary colours on the
butterfly come from the
interaction of light on the
nanometre size structures on
their wings.
• The same effect can be seen on a
CD when you tilt it.
Let’s take a closer look at the butterfly
Here
issection
a colour
clearer
image
of the
thecan
scales
taken
using
an
AIf
cross
of of
these
ridges
show
The
we true
take
a closer
look
the wings
at
scales,
bethe
seen
wenanostructures
can
when
seelight
ridges.
is
The
iridescent
colours
on
its
wings
are
not
created
by
electron
microscope.
The
scales
on
the
wings
are
that
reflect
the
The
microribs
are
shaped
like
Each
passed
ridge
through
is light.
approx.
the
800
wing
nm
butwide
not
and
reflected.
contains
The
blue
morpho
butterfly
is
native
of
central
and
south
pigments,
but
by
the
way
light
interacts
with
the
nano
arranged
tiles
onisaknown
roof.
is approx.
70 x
evergreen
trees
(short
branches
atscale
the
long
branches
structures
thatEach
reflect
thetop
light.
America,like
the
male
for
its
iridescent
blue
colour.
structures
on the
scales.
200
µm.
at the base)
allowing
for wings’
multiple
reflections.
Applications
Scientists are using their understanding of the structure of butterfly
wings to develop new fabrics, dye-free paints, and anti-counterfeit
technologies for currency.
Summary
• Natural nanomaterials are inspiring scientists!
• Lotus effect:
– Self-cleaning windows.
– Waterproof clothing.
• Gecko feet:
– Adhesives.
• Spider silk and caterpillar cocoons:
– Stronger, lighter materials.
• How many more natural nanomaterials can you remember?